Businessman John Brunner (R) holds a big lead over his primary opponents, according to a new internal poll released by his campaign.

Brunner leads with 40 percent of the vote to 20 each for Rep. Todd Akin (R-Mo.) and former Missouri state Treasurer Sarah Steelman (R). While internal polls should always be viewed with a bit of skepticism, this is a good sign for Brunner's campaign in a muddled race where the three candidates are close on policy views.

The wealthy businessman has been spending heavily to boost his name identification in the state.

The poll of 600 likely primary voters was conducted by GOP pollster American Viewpoint from June 19 through 21 and had a margin of error of plus or minus 4 percentage points.

The winner of the August primary will move on to face vulnerable Sen. Claire McCaskill (D-Mo.). The Hill rates the race a "toss-up."